Prostheses are connected to dental implants by attaching to an intermediary device that fits inside the implant. This device is called an abutment and it is generally placed into the implant between 6 and 12 weeks after implant surgery. Full arch prostheses connected to implant abutments are generally made with a metal substructure supporting a resin denture base material such as poly(methyl methacrylate) (PMMA) and artificial plastic teeth. The denture base and denture teeth comprise the prosthesis suprastructure. The metal alloys used for substructure fabrication exhibit very high rigidity. The metal substructure is able to resist overall distortion when the PMMA is added (polymerized) even though the PMMA exhibits very high polymerization shrinkage. However, among other concerns, metal alloys are unaesthetic and cannot form a chemical bond to the resin substructure materials. The use of fiber composite technology in the creation of a metal-free implant prosthesis may solve many of the problems associated with this metal alloy substructure such as corrosion, toxicity, complexity of fabrication, high cost and esthetic deficiencies. Prosthesis fabrication generally begins shortly after abutment placement. Due to the many steps and complexity of implant prosthesis fabrication, it usually takes weeks to months to complete. Therefore, the patient cannot benefit from the final implant prosthesis for an extended period of time.
Light polymerized glass fiber-reinforced composites (FRC)s have been developed that have the potential to make an esthetic implant prosthesis substructure utilizing a simple, time-efficient technique. Laboratory and clinical research evaluating FRC prostheses used to restore and replace teeth has shown that these materials exhibit excellent mechanical properties and can form a chemical bond to resin-based denture base materials. While the use of FRC materials for substructure fabrication offers important advantages over the use of metal alloy substructures, problems with this approach have been identified. Laboratory testing has shown that FRC materials used to make the prosthesis substructure exhibit very little polymerization shrinkage resulting in excellent dimensional stability of the substructure with no apparent misfit at implant abutment interface areas. However, FRC materials are not as rigid as metal alloys. Consequently, laboratory testing has also shown that the polymerization of PMMA denture base material with embedded denture teeth over this dimensionally stable FRC substructure results in measurable distortion due to the expected high polymerization shrinkage of the PMMA.
This finding was a great concern. From the data obtained in the laboratory and clinical studies, the inventors determined that there was measurable error in the dimensions of the prosthesis when the PMMA denture base and denture teeth were polymerized to the substructure using a standard heat processing technique. This technique is typical for the fabrication of complete dentures or during the placement of PMMA on removable partial dentures or metal supported full arch implant prostheses.
A noteworthy prosthesis misfit should result in “rocking” or lack of stability of the prosthesis when placed in the mouth and an increased likelihood of screw loosening after prosthesis placement. Tightening the fastening screws that attach the prosthesis to the abutments can generally eliminate the slight misfit observed at the prosthesis/abutment interface. While the tightening of the prosthesis fastening screws eliminates any misfit at the abutment/cylinder interface, this may result in high internal strain within the prosthesis, likely at the suprastructure/substructure interface. Consequently, there is potential for long-term clinical problems due to prosthesis distortion upon suprastructure polymerization.
Additional problems associated with implant prostheses are the breakage and debonding of denture teeth with clinical usage. There is much evidence that this is a universal problem associated with full arch implant prostheses regardless of whether metal alloy or FRC are used for the substructure material. Denture teeth were designed and manufactured to be placed on removable prostheses. Patients are unable to place high loads on these removable prostheses due to their soft tissue support. Also, denture teeth bond poorly to the PMMA that they are placed into. This results in the need to place mechanical retention into the underside of the denture teeth, which further compromises their strength. This is the case for all implant prostheses, not just FRC implant prostheses.
There is a need to provide strong denture teeth to withstand the stresses in a patient's mouth. It would also be beneficial to provide a bonding mechanism to enable denture teeth to adhere strongly to the denture base without the need to grind or machine the teeth to create mechanical retention. It would be advantageous to minimize or eliminate full arch FRC implant prosthesis distortion. It would certainly be preferable to provide a prosthesis for attachment to implants in a time period shortly or immediately following surgical placement of the implants in a patient's mouth.